The invention also relates to a method of drilling a bore hole into a subterranean earth formation.
A percussive shearing drill bit is known and described in U.S. Pat. No. 6,253,864. FIG. 9 of said U.S. Patent depicts a percussive drill bit having dome shaped axial cutters optimised for percussive penetration of the earth formation, and shear cutters optimised for shear penetration.
In operation, the known percussive shearing drill bit is rotated about its longitudinal axis shearing off the rock formation as the drill bit rotates. A hammer simultaneously impacts the bit thereby providing an additional percussive drilling force.
It is seen as a disadvantage of the known percussive shearing drill bit that, notwithstanding the presence of axial cutters, the shear cutters still are subject to impact blows that may shorten their lifetime and consequently that of the drill bit.